1. Field of the Invention
The present invention generally relates to hand tools and, more specifically, to improved automatically adjustable pliers.
2. Description of the Prior Art
Numerous self-adjusting slip-joint pliers have been proposed. Such pliers share a number of common characteristics, including jaws that are offset at an angle to the longitudinal direction of the handles, and a pivot post in the form of a bolt or rivet mounted on the jaw of one of the handles and projecting through an elongated slot or channel on the other handle. In such pliers, the distance or the spacing between the work-gripping jaws is adjusted by a number of different designs, such as spaced apart ridges or teeth along the inside long edge of the slot adopted to selectively engage the pivot post. Another one of the methods for providing distance adjustment between the jaws in such pliers is to provide spaced-apart arcuate ridges on the interfacing surfaces adjacent the pivot point. All such tools have the common objective of adjusting to the size of the particular work piece to be gripped between the jaws. Typically, the use of such tools has required a two-handed operation wherein the handles are pulled wide apart to permit a sliding action of the pivot post along the slot to move the jaws into contact with the desired work piece.
In some cases, the pliers have been constructed for single-handed adjustments. Such pliers are adapted to slidably close on a work piece in response to manual closing action of the handles. The pliers automatically lock in response to contact of the jaws with the work piece against further sliding action and shift from a sliding to a pivoting mode in which continued exertion of manual force on the handles causes increased gripping action on the work piece. Such a pliers is disclosed in U.S. Pat. No. 4,651,598, and, aside from the sliding action of the bolt through the channel prior to engagement of a work, the pliers' movable or operative parts are limited to only one degree of freedom of linear movement after the work has been gripped between the jaws. This limitation severely restricts the adjustability for compensating for different sized works and bringing the jaws and handles into alignment.
In U.S. Pat. No. 4,662,252, an auto-grip pliers is disclosed which is capable of automatically adjusting the distance between the gripping jaws in relation to the size of the work piece to be gripped. The pliers utilizes one or more hidden springs to cause the automatic adjustment function. In this patented design the handle members are interconnected by a cross over linking arm. The linking arm is a rigid planar part having a first end normally positioned against a stop as a result of the pulling force of a spring within one of the handles. The other end of the linking arm is pivotally mounted on the other handle. Unlike many slip joint pliers, which are usually mass produced by drop forging operations, in which the handles and the jaws are made of solid metal, the pliers disclosed in this patent are formed of stamped metal parts which, in some cases, are laminated to form thicker pliers elements, as required. As with the previous patent, the operative parts of the pliers are limited to a single degree of freedom of movement after the work has been engaged.
Another automatically slidably adjustable pliers tool is disclosed in U.S. Pat. No. 4,893,530, in which the jaws can be automatically adjusted in response to the closing of the handles to the size of any workpiece or other item to be gripped within a size range defined by the maximum opening between the tool jaws. As with the tool disclosed in the previously mentioned patent, a rigid control arm extends from one handle to the other handle, the arm being pivotally mounted on one of the handles and pivotally and slidably mounted on the other handle. Again, as with the previously described patents, the ability to bring the jaws and handles into substantial parallelism is severely restricted by a single degree of freedom of linear movement of the operative parts after the work is engaged.
The known self-adjusting pliers have all had a number of disadvantages. First, while some of these known pliers have attempted to effect an adjustment of at least one of the jaws to bring the jaws into substantial parallel alignment following the shift from the sliding to the pivoting mode, the known constructions have not had the self-adjusting range to effect parallel jaw gripping surface alignment but for a small range of sizes of works. For works outside of the range the jaw surfaces have either undercompensated or overcompensated, depending on the specific design, and the target range of work sizes intended to be gripped by the jaws. Another disadvantage of prior art adjusting pliers has been that the handles have been variably spaced when gripping differently sized works. For large works, for example, the handles are typically spaced greater than a desired spacing for optimum gripping of the handles by the hands of a user, thus preventing the user from comfortably gripping the pliers and transmitting the maximum amount of force to the handles. Ideally, the handles should always settle at an optimum position in which the handles are spaced a desired distance apart and are substantially parallel to each other for all sizes of works. Again, because known pliers have not had the sufficient adjustability range to equally accommodate different sized works, they have not been able to provide the optimum handle spacing and parallelism but for a very small range of sizes of works.
One of the objectives of all pliers is to be able to grip the work with sufficient force so that there is no slipping between the work and the surfaces of the jaws. This sometimes requires substantial application of force on the handles of the pliers and on the jaws. Generally, the more force that is applied by the jaws to the work the less likely that slipping will occur, particularly when the jaw gripping surfaces are parallel to each other while gripping the work. However, known adjustable pliers are typically simple, single pivot lever devices where the mechanical advantage gained can be readily computed by comparing the lengths of the handles or arms to which the forces are applied and the sizes of the jaws and the points of application of force by the jaws to the work. Unfortunately, the mechanical advantage offered or provided by such known pliers has sometimes been insufficient to result in the desired forces being applied to the work based on the maximum forces that the user can apply to the handles. The inability to apply sufficiently high forces to the work, as aforementioned, may result in slipping between the jaws and the work and even injury to the user or damage to the work itself.